This invention relates primarily to combustor chambers and, more particularly, to an air-cooled combustion liner for a gas turbine engine and a method of making the same.
Increased performance levels of gas turbine engines can be obtained by increasing the operating temperatures thereof. In so doing, the combustion chambers of these gas turbine engines are exposed to extremely high temperatures which would be destructive to the combustor apparatus unless some precautions are taken. Although there have been great improvements in liner alloys and other combustion chamber materials in order to allow higher temperature operation, a common method of enhancing combustion chamber life and dependability is to cool the combustion chamber by way of cooling air circulation.
One of the most successful methods of cooling combustor liners is that of film-surface cooling, wherein a thin layer of cooling air is formed between the hot gases of combustion and the liner portions forming and defining the combustion chamber. Typically, the combustion chamber liner defining a combustion zone also partially defines a cool fluid plenum usually circumscribing the combustion zone. Means are commonly provided for transferring a portion of the cool fluid from the plenum into the combustion zone to form the protective film barrier on the inner surface of the combustion liner. Formed in the liner walls are a plurality of holes or slots which are axially spaced to assure that a sufficient amount of air is distributed along the entire length of the liner. The amount of cooling air which is eventually used is detrimental to combustor performance characteristics and is therefore preferably held to a minimum. This minimal use of cooling air results in acceptable liner life so long as nothing occurs in the operation thereof which would result in local or continuous interruption of the film cooling. In order to obtain effective film propagation over the entire inner surface of the liner, the air which enters the combustor liner from the surrounding plenum must be directed in such a manner as to attach to the inner surface of the liner so as to form a boundary layer without aspirating or entraining hot gases from the combustion zone. In providing the proper fluid flow direction, it has become common to utilize a relatively long, axially extending, overhanging lip to define, along with the liner inner side, a slot to properly direct the fluid flow.
One difficulty which has been experienced from the use of an overhanging lip is that a decay of the cooling film allows the slot overhang to tend to overheat, and since it is relatively thin and unsupported at its discharge end, it tends to grow radially outward so as to close off the cooling slot. This results in a reduction of cooling flow and further overheating of slot overhangs which are disposed downstream therefrom.
In order to overcome the blockage of coolant flow by thermal growth of the lip, the lip may be made of heavier material which will resist the thermal stresses resulting from the cooling film decay. However, the advantages of using heavier material for the forming of the overhanging lip may very well be offset by the disadvantages of increased weight and cost of manufacture.
It is therefore an object of the present invention to provide a combustor liner which provides a continuous, uninterrupted film of cooling air on the inner side thereof.
Another object of this invention is the provision for a combustor liner which is capable of operating under high temperature conditions over a long life period.
Yet another object of this invention is the provision for a combustor liner which is economical to fabricate and extremely effective in use.
These objects and other features and advantages will become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.